Study of electromagnetic decays of orbitally excited Ξc baryons

Using 980 fb−1 of data collected with the Belle detector operating at the KEKB asymmetric-energy eþe− collider, we report a study of the electromagnetic decays of excited charmed baryons Ξcð2790Þ and Ξcð2815Þ. A clear signal (8.6 standard deviations) is observed for Ξcð2815Þ0 → Ξ0 cγ, and we measure: B½Ξcð2815Þ0 → Ξ0 cγ B½Ξcð2815Þ0 → Ξcð2645Þþπ− → Ξ0 cπþπ− ¼ 0.41 0.05 0.03. We also present evidence (3.8 standard deviations) for the similar decay of the Ξcð2790Þ0 and measure: B½Ξcð2790Þ0 → Ξ0 cγ B½Ξcð2790Þ0 → Ξ0þ c π− → Ξþ c γπ− ¼ 0.13 0.03 0.02. The first quoted uncertainties are statistical and the second systematic. We find no hint of the analogous decays of the Ξcð2815Þþ and Ξcð2790Þþ baryons and set upper limits at the 90% confidence level of: B½Ξcð2815Þþ → Ξþ c γ B½Ξcð2815Þþ → Ξcð2645Þ0πþ → Ξþ c π−πþ < 0.09, and B½Ξcð2790Þþ → Ξþ c γ B½Ξcð2790Þþ → Ξ00 c πþ → Ξ0 cγπþ < 0.06. Approximate values of the partial widths of the decays are extracted, which can be used to discriminate between models of the underlying quark structure of these excited states.